DE19751397A1 - Steering system operating method for motor vehicles - Google Patents

Abstract

The method is for an override system with actuating drive and override transmission. The transmission superimposes a first movement, and a second movement initiated by the drive due to energy supply. Standstill of the actuating drive is recognized, and as a result, the energy supply is reduced to zero, interrupted, or switched off. The time variation in the movement initiated by the drive, is measured and recognized dependant upon the variation. Standstill is esp. recognized when the variation has reached a set value, esp. zero.

Description

State of the art

The invention is based on a method or a method direction for operating a superimposition or steering system, in particular for a motor vehicle, with the features of General terms of the independent claims.

Such a steering system is known from DE-OS 40 31 316 (corresponds to US 5,205,371) and, insofar as it is relevant for understanding the present invention, is to be explained with reference to FIGS . 1 and 2. In such a steering system, the steering movements applied by the driver through the steering wheel 11 or 21 , the steering wheel angle δ _L detected by the sensor 28 , in the superposition gear 12 or 22 with the movements, the motor angle δ _M , the actuator bes 13 or 23 overlaid. The resulting total movement δ _L 'is transmitted via the steering gear 14 or the steering linkage 16 to the steerable wheels 15 a and 15 b for setting the steering angle δ _V. Here, the Stellan drive 13 or 23 can be designed as an electric motor, the drive from the electric motor via a self-locking Ge gear takes place so that the motor can not be rotated by acting in the Lenkwel le torques. Such a steering system can be used as a power steering system in that the steering can be made very indirectly by the translation i _{ü of} the Überlagerungsge gear 12 or 22 and since low steering wheel torques M _L can be achieved. Since conditional, very large steering wheel angles δ _L are avoided by overlaying suitable motor angles δ _M , so that according to the context

δ _L '= δ _L / i _ü + δ _M

required output angle δ _L 'can be set with steering wheel angles of conventional size. The motor angle δ _M required for steering assistance or its target value is determined from the steering wheel angle δ _L. In addition, the motor angle δ _{M can be selected} to influence the dynamic behavior of the vehicle additionally or exclusively depending on signals Sm, these signals Sm representing the vehicle movements detected by the sensors 26 . Then the gear ratio can also be i _ü = 1.

In a steering system described above, the additional steering angle δ _M must generally take constant values, in particular zero, over longer times. If the constant value of the motor z. B. due to friction not set exactly, a constant continuous current flows, which disadvantageously leads to the heating of the motor and unnecessarily consumes electrical energy. This problem, which is presented using a steering system, can occur with all actuators and drives with self-locking, for which the output variable (angle, position) should assume constant values for longer periods.

The object of the present invention is this To eliminate the disadvantage.

This task is carried out by the combinations of features of the independent pending claims resolved.

Advantages of the invention

As mentioned with the aid of a steering system, the invention proceeds of an overlay system with an actuator and a superposition gear, being through the superposition gear a first movement and one by the actuator initiated by an energy supply to the actuator second movement can be overlaid. The one from the actuator initiated movement is via a self-locking mecha nism fed to the superposition gear. The core of the Er Invention is that the actuator stops is recognized and in response to a detected standstill the energy supply to the actuator is at least reduced becomes.

A special implementation of the general invention his thoughts are based on a power steering system vehicle with at least one steerable wheel, a Stellan driven and a superposition gear. Through the overlay The transmission is initiated by the driver of the vehicle ized steering movement and the one initiated by the actuator Movement to generate the steering movement of the steerable wheel overlaid by a self-locking mechanism. The Stell Drive is energized to initiate the movement leads. The essence of the invention is that a still position of the actuator is recognized and in response to egg  The standstill recognized the energy supply to the Stellan drive is at least reduced. To avoid the above mentioned heating of the actuator and to prevent egg unnecessarily high energy consumption of the actuator thus according to the invention the energy supply of the actuator at least reduced, especially interrupted or shuttered when the actuator stops.

The energy supply to the actuator can be so re be reduced that the current supplied to the actuator is reduced, in particular a reduction to the value zero, i.e. when the Stellan is switched off drive is thought.

In an advantageous embodiment it is provided that the change over time of those initiated by the actuator Movement is detected and the actuator is at a standstill depending on the detected change in time is detected. The standstill of the actuator can then be detected when the time change a certain value, in particular the value zero.

Furthermore, it can be provided that the energy supply to the Actuator is at least reduced when the still the actuator was recognized for a selectable period of time has been. This has the advantage that a reduction in Only then supply or switch off the actuator happens when it is not expected that by a wide The desired angle is inserted even more precisely is posed.  

It is particularly advantageous that the actuator initiated movement is detected and a setpoint for the movement initiated by the actuator and the differences limit between the setpoint and the movement is determined. Then at the time of the reduction according to the invention the difference determined in this way is saved. Here is esp special provided that the reduced energy supply then is increased again when the currently determined difference is the stored difference over or a predetermined amount steps.

It is also advantageous to add the stored difference error detection. In particular is there provided that the stored difference with at least a predefinable threshold is compared and depends on an error signal is given to the comparison result. This Design has the background that when the Stell drive shows a larger control deviation for a long time, this is due to an error due to increased friction or Clamps in the actuator or gear can indicate. In this case can also be a fault in the actuator hearing current regulator, the power electronics or the ener energy supply available. Breastfeeding can cause such anomalies Report the shutdown to a safety monitor, the then initiates suitable test or emergency measures.

Furthermore, it can be provided that the by the Stellan drove initiated movement while reducing the ener Giezufuhr recorded and used for error detection becomes. In particular, it is provided that an error i gnal is generated when the during the reduction of the Initiated movement energy input captured by a forward  definable measure changes. This is because a changing measured value of the additional steering angle during shuttering on an error of the corresponding sensor or an serious errors in the engine or transmission such as B. Ver say the self-locking indicates. Such anomalies can Standstill shutdown to a safety monitoring mel the one who then takes appropriate emergency measures.

In addition to the method according to the invention, the invention relates also the corresponding devices.

Further advantageous refinements are the dependent claims Chen to take.

drawings

Figs. 1 and 2 schematically show the steering system of the prior art from which the invention proceeds in the embodiment. FIG. 3 shows the control or regulating strategy of such a steering system with the position controller depicted in FIG. 4. FIG. 5 shows the position controller according to the invention with the signal curves shown in FIG. 6.

Embodiment

In the following, the invention is to be described with reference to an embodiment are shown in a game. An example of one overlap steering mentioned at the outset.

Fig. 1 and Fig. 2 shows an actuatable by the driver of the vehicle steering wheel by the reference numerals 11 and 21 respectively. By actuating the steering wheel 11 or 21 , the gearbox 12 or 22 is supplied via the connection 101 to the steering wheel angle δ _L. At the same time, the superposition gear 12 or 22 is supplied with the motor angle δ _{M of} the actuator 13 or 23 via the connection 104 . Here, the actuator 13 or 23 can be designed as an electric motor, the drive from the elec tromotor via a self-locking gear so that the motor cannot be rotated by torques acting in the steering shaft.

On the output side of the superposition gear 12 or 22 , the total movement δ _L 'is fed via the connection 102 or 103 to the steering gear 14 or 24 , which in turn via the steering linkage 16 corresponds to the total angle δ _L ' of the steerable wheels 15 a and 15 b with the steering angle δ _V applied. In FIG. 2 sensors continue to see 28 and 26, wherein the sen sor 28 the steering wheel angle δ _L is detected and the control unit supplies 27, while 26 sensors are gekennzeich net with the reference numerals which the movements of the vehicle 25 (eg. Gierbewe conditions, lateral acceleration, vehicle speed, etc.) sen and the corresponding signals Sm to the control unit 27 . The control unit 27 determines, depending on the detected steering wheel angle δ _L and possibly depending on the vehicle movements, a manipulated variable u (output variable of the control unit 27 ) for controlling the actuator 13 or 23 .

Fig. 3 shows a block diagram of the function of the steering system while driving the vehicle. The steering wheel angle δ _L detected by the sensor 28 is fed to the steering aid control 41 for this purpose. Depending on the steering wheel angle δ _L and possibly depending on the detected longitudinal vehicle speed V _x, the power steering control 41 determines a steering component δ _MLH . Dane ben determined the vehicle controller 44 depending on the detected vehicle movements by the sensors 26 (longitudinal vehicle speed V _x, yaw rate ω, lateral acceleration, etc.) a further dynamic steering proportion δ _corr. The steering component δ _MLH , which takes the steering assistance function into account, and the steering component δ _Korr , through which the vehicle dynamics of the vehicle are optimized, are superimposed at point 45 to a target motor angle δ _{M, which is} fed _to the position controller 42 on the input side. Furthermore, the position controller 42 is the current motor angle δ _M, the motor 13 or 23 is supplied. Depending on ei nem target-actual comparison determines the subordinate position controller 42 the target motor current I _should. Due to the deviation of the target motor current I _soll and the motor detected at the vehicle engine 13 or 23 actual current I _(subtracting 46) determines the current controller 43, a corresponding control signal u for the servo motor 13 or 23, δ to the desired motor angular _{M , is supposed} to be realized.

As a position controller, a controller 42 a with a proportional and a differential component (PD controller) according to FIG. 4 is used. This PD controller receives the actual value for the motor angle δ _M, as well as the corresponding setpoint δ _{M, should} . From these two input variables δ _{M, ist} and δ _M, the time derivatives are to be formed in the differentiating units 50 and 54 and weighted in the amplification stages 52 and 53 with different amplification factors K _Ds and K _Di , where in particular K _Ds = 0 . At point 55 the difference is then determined between these obligations Ablei weighted and the weighted (gain stage 51, gain K _p) control deviation (δ _{M, to} -δ _{M is)} superimposed to the target motor current I _soll.

The use of such a controller without an I component has the advantage that the quite high friction of the self-locking gear cannot lead to limit cycles. This results in permanent control deviations, in particular if the constant δ _M remains _, the motor 13 , 23 _should stop due to the friction before the actual value δ _M, the target value δ _{M, is} reached. A constant motor current is set via the P-channel of the position controller (gain K _p ), which is so small that the friction is not overcome and the motor does not continue to rotate. This current only heats the engine.

Fig. 5 shows the position controller 42 a with the inventive extension by a shutdown. This is also the PD controller already described with the differentiating units 50 and 54 and amplification stages 51 , 52 and 53 also described. New is the switch 56 , the switching state of which is changed by the switching signal S and by opening the motor current or, via the current regulator 43, the motor voltage u is reduced to the value zero and the motor 13 , 23 is switched off.

The block denoted by 13 , 23 in FIG. 5 can of course also be the current regulator 43 shown in FIG. 4 or in FIG. 3. In this case, the current regulator 43 _is supplied with the target current I des.

The switching signal S is formed in the standstill shutdown 57 .

The input variables of the standstill shutdown 57 are the control deviation e = δ _M, target -δ _M, and the change in the motor angle δ _{M, ist} (= δ _M ) or the engine speed

The function of the shutdown shutdown is shown in FIG. 6 by way of example on the basis of time profiles of the essential variables. It is assumed that the motor should return from a positive angle δ _M (curve marked with lines) to zero angle, ie it is at the beginning of the period under consideration

The motor 13 , 23 follows the setpoint, ie

which results in a certain following error. As a result of the following error and the friction, the motor stops at time t ₀ before δ _M = δ _M, Soll = 0. This means that from time t ₀

is. The existing control deviation e (curve marked with dashes and dots) leads to the above-mentioned constant motor current I _soll for t <t ₀ .

The standstill shutdown 57 now recognizes at time t ₀ from the change in δ _M or the speed

that the engine 13 , 23 is stopped. In order to avoid impairments of movements with rapid zero crossings of the setpoint speed, the standstill switch-off 57 waits for a certain time Δt after the motor has come to a standstill. When the engine during all this time is, it is at the time t ₁ = t ₀ + .DELTA.t switched off, it ie I _soll = 0 is set and the switch 56 is given in Fig. 5 tet vice stale.

For switching the motor 13 , 23 back on , a threshold is established from the control deviation e (t ₁ ) at the time t _{1 of} the switching off

e ₀ = | e (t ₁ ) | + ε

formed with the positive constant value ε. If the control deviation e exceeds the band defined by ± e ₀ , ie if | e (t) | <e ₀ , the motor is switched on again by control S of the switch 56 , ie the current setpoint I _intended by the PD controller _{is to be switched} through. If the system functions properly, this can only be done by changing the setpoint δ _M, nominal. In the example considered, it is assumed that δ _{M, should} rise again from time t ₂ and the control deviation e at time t ₃ exceeds the band ± e ₀ , so that the motor is switched on again or energized at time t ₃ and starts up.

A major advantage of this shutdown shutdown be is that no knowledge of the existing in the system Frictional forces and frictional relationships are required. That's why protects the motor and power electronics standstill shutdown Technology and on-board electrical system from high long-term loads even in the absence If the motor or the gearbox jams.

In addition, the described standstill monitoring 57 can also be used for fault detection. If the threshold e ₀ assumes unusually large values, this is a sign of increased friction or jamming in the motor or gearbox or for faults in the current controller, the power electronics or the energy supply. In the standstill monitoring 57 it can therefore be provided that the value e _{0 is} compared with an additional threshold. If e ₀ exceeds the threshold, an error is displayed via error detection 501 or signal lamp 502 .

If the measured value δ _M of the engine angle changes while the engine is switched off, this indicates an error in the sensor, which senses the engine angle δ _M as δ _M, or a serious error in the engine or transmission such as. B. on the failure of self-locking. Such anomalies can report the shutdown shutdown 57 to a safety monitor 501 , which then initiates suitable emergency measures, for example activation of the signal lamp 502 .

The use of the PD controller 42 a with the standstill circuit 57 does not necessarily require the use of a subordinate current controller 43 , as shown in FIG. 3. The arrangement can also directly determine a motor voltage u. The above statements apply accordingly.

In summary, the following points should be mentioned as the core and advantages of the invention:

• - The servomotor is switched off when it comes to a standstill and the position control deviation e is so small that that of Position controller set motor current to restart the Motors is not enough.
• - Reactivation of the motor in the event of a larger control deviation e.  
• - Prevention of excessive engine warming.
• - Saving electrical energy.
• - The function according to the invention is fulfilled solely on the basis of the signals present in the position controller 42 a.
• - The function according to the invention is carried out autonomously by the position controller 42 a extended by the standstill shutdown 57 ; higher-level functional units such. B. Vehicle controller 44 do not have to intervene. This facilitates a modular structuring of the functions.
• - The function of the invention is without prior knowledge of Friction conditions fulfilled.
• - The function according to the invention is also in the event of an error increased friction or jamming in the engine or transmission fills. This results in an effective one in this case Protection of engine, power electronics and vehicle electrical system.
• - The standstill shutdown 57 can detect certain faults in the motor, gearbox, current controller, power electronics, power supply or motor angle sensor and report it to a safety monitor 501 , 502 .

The be in the embodiment using a steering system written shutdown can not only be for the wrote steering system find use but for everyone Actuators and drives with self-locking are used at which the output size (angle, position) for longer time ten should assume constant values.

Claims (12)

1. A method for operating a superimposition system with an actuator ( 13 ; 23 ) and a superimposition gear ( 12 ; 22 ), wherein a first movement (δ _L ) and one through the actuator ( 13 ; 23 ) by an energy supply ( I _should , u) to the actuator initiated second movement (δ _M ) are superimposed and the movement initiated by the actuator is fed to the superposition gear via a self-locking mechanism, characterized in that a standstill of the actuator is recognized and in response to one detected standstill the energy supply (I _should , u) to the actuator is at least reduced. 2. Method for operating a steering system for a motor vehicle with at least one steerable wheel ( 15 ), an actuator ( 13 ; 23 ) and a superposition gear ( 12 ; 22 ), the steering movement initiated by the driver of the vehicle (δ _L ) and the movement (δ _M ) initiated by the actuator ( 13 ; 23 ) by an energy supply (I _soll , u) to the actuator for generating the steering movement of the steerable wheel and the movement initiated by the actuator via a self-locking mechanism the superposition gear is supplied, characterized in that a standstill of the actuator is detected and in response to a known standstill the energy supply (I _should , u) to the actuator is at least reduced. 3. The method according to claim 1 or 2, characterized in that in response to a detected standstill of the actuator drive the energy supply (I _should , u) to the actuator is reduced to zero or interrupted or switched off. 4. The method according to claim 1 or 2, characterized in that the temporal change
the movement initiated by the actuator (δ _M ) is detected and the standstill of the actuator is detected depending on the detected change in time, it being provided in particular that the standstill of the actuator is recognized when the change in time is a certain value, in particular the Value zero, reached. 5. The method according to claim 1 or 2, characterized in that the energy supply (I _should , u) to the actuator is then at least reduced when the standstill of the actuator has been recognized for a selectable period of time. 6. The method according to claim 1 or 2, characterized in that the energy supply (I _soll , u) to the actuator is reduced such that the current supplied to the actuator is reduced, in particular to the value zero. 7. The method according to claim 1 or 2, characterized in that the movement initiated by the actuator (δ _M ) it is detected and a setpoint (δ _M, target) for the movement initiated by the actuator (δ _M ) and the difference (e) between the setpoint (δ _M, Soll) and the movement (δ _M ) is determined and the determined difference [e (t ₁ )] is stored at the time (t ₁ ) of the reduction. 8. The method according to claim 7, characterized in that the reduced energy supply is increased again when the currently determined difference exceeds or falls below the stored difference [e (t ₁ )] by a predeterminable amount (ε). 9. The method according to claim 7, characterized in that the stored difference [e (t ₁ )] is used for error detection, it being provided in particular that the stored difference [e (t ₁ )] is compared with at least one predetermined threshold and an error signal (F) is emitted depending on the comparison result. 10. The method according to claim 1 or 2, characterized in that the movement initiated by the actuator (δ _M ) is detected and the detected during the reduction of the energy supply initiated movement (δ _M ) is used for an error detection, in particular it is provided that an error signal (F) is generated when the initiated movement (δ _M ) detected during the reduction in the energy supply changes by a predeterminable amount. 11. Device for operating a superimposition system with an actuator ( 13 ; 23 ) and a superposition gear ( 12 ; 22 ), with a first movement (δ _L ) and one through the actuator ( 13 ; 23 ) by an energy supply (I _should , u) to the actuator initiated second movement (δ _M ) are superimposed and the movement initiated by the actuator is fed to the superposition gear via a self-locking mechanism, characterized in that means ( 57 ) are provided for detecting a standstill of the actuator are, by means of which the energy supply (I _soll , u) to the actuator is at least reduced in response to a detected standstill. 12. Device for operating a steering system for a motor vehicle with at least one steerable wheel ( 15 ), an actuator ( 13 ; 23 ) and a superposition gear ( 12 ; 22 ), the steering movement initiated by the driver of the vehicle (δ _L ) and the movement (δ _M ) initiated by the actuator ( 13 ; 23 ) by an energy supply (I _soll , u) to the actuator for generating the steering movement of the steerable wheel and the movement initiated by the actuator via a self-locking mechanism is fed to the superposition gear, characterized in that means ( 57 ) are provided for detecting a standstill of the actuator, by means of which the energy supply (I _soll , u) to the actuator is at least reduced in response to a detected standstill.